Gas flow regulation for electric precipitators

ABSTRACT

A horizontal, dry-type electric precipitator is provided with one or more gas flow diverter units located between the inlet and outlet and extending across the precipitator chamber to increase the gas flow near the top of the chamber relative to the flow near the bottom. Each diverter unit is constituted by, for example, resistance baffles spaced to leave graded openings, an orifice plate with graded openings, or baffles inclined at graded angles. Where more than one diverter unit is provided, the gradation of succeeding units is such as to provide a higher gradation of flow rate, the farther downstream the unit is located.

United States Patent 1 Gallaer [54] GAS FLOW REGULATION FOR ELECTRIC PRECIPITATORS [75] Inventor: Charles A. Gallaer, Palmyra, Pa.

[73] Assignee: Envirotech Corporation, Salt Lake 7 City,Utah

[22] Filed: Feb. 4, 1971 [21] Appl. No.: 112,541

[52] U.S. Cl ..55/129, 55/136 [51] Int. Cl ..B03c 3/36 [58] Field of Search ..55/l12, 128, 129, 55/130,136,137,l38, 143,145, 154, 124, 126

[56] References Cited UNITED STATES PATENTS 2,634,818 4/1953 Wintermute ..55/ll2 2,712,858 7/1955 Wintermute ..'.55/443 X 111 3,733,785 [451 May 22,1973

FOREIGN PATENTS OR APPLICATIONS 5 228,915 6/l960 Australia ..55/l24 565,152 10/l933 Germany ..55/112 Primary Examiner-Dennis E. Talbert, Jr. Attorney-Robert R. Finch and'Robert E. Krebs [57] ABSTRACT A horizontal, dry-type electric precipitator is provided with one or more gas flow diverter units located between the inlet and outlet and extending across the precipitator chamber to increase the gas flow near the topof the chamber relative to the flow near the bottom. Each diverter unit is constituted by, for example, resistance baffles spaced to leave graded openings, an orifice plate with graded openings, or baffles inclined at graded angles. Where more than one diverter unit is provided, the gradation of succeeding units is such as to provide a higher gradation of flow rate, the farther downstream the unit is located.

21 Claims, 7 Drawing Figures PATENTE w 2 2197s SHEET 1 IF 3 INVENTOR CHARLES A GALLAER BY $4 111., flaw g,

his ATTORNEYS PATENTEU HAY22I973 INVENTOR.

CHARLES A. GALLAER &

his ATTORNEYS PATENTED HAY 2 21975 SHEET 3 OF 3 QOCDOO GQQOC) ""000 O O 0 GO FIG? INVENTOR.

CHARLES A. GALLAER his ATTORNEYS GAS FLOW REGULATION FOR ELECTRIC PRECIPITATORS BACKGROUND OF THE INVENTION This invention relates to electric precipitators and, more particularly, to a gas flow control system for horizontal, dry-type precipitators.

Electric precipitators are widely used to remove fine dust particles that are suspended in air or other gases.

One type of precipitator, commonly known as the Cottrell type, involves single-stage ionization and collection; that is, the particles are collected in the same electric field in which they are charged or ionized. The invention has particular applicability to Cottrell type precipitators, but also can be applied effectively with other types, such as two-stage units where the particles are charged in one field and collected in another.

In the conventional Cottrell type precipitator, banks of corresponding emitting and collecting electrodes extend across a flow chamber. Each emitting electrode is charged to a relatively high DC voltage, and the resulting electrical field between the emitting and collecting electrodes ionizes the suspended dust particles in a stream of dust-laden gas conducted through the flow chamber. The particles are charged with the same polarity as the emitting electrodes and are attracted to the collecting electrodes, which are oppositely charged, and accumulate on them. Periodically, the collecting electrodes are rapped or vibrated, causing the accumulated particles to become dislodged and fall by gravity into collecting bins or hoppers located at the bottom of the precipitator chamber.

In order to reach the hopper, the average dislodged particle must fall from its point of deposition on a collecting electrode a mean distance of one-half the height of the precipitator (for example, feet in a 30 foot high precipitator). One problem encountered in a drytype horizontal flow precipitator is that the particles, because they are small in size, tend to be reintroduced into the flow of gas through the chamber, i.e., reentrained, and must be removed again by the same process described above at an emitter-collector pair farther downstream.

Many attempts have been made to minimize reentrainment and thereby increase operational efficiency, but with only marginal success. The improvements have been mainly directed to providing different sizes and shapes of electrodes and various ducting techniques. However, in these modified precipitators the cross-sectional velocity of the stream of gas flowing through the precipitator chamber has been maintained at a substantially uniform level along the entire length of the flow chamber.

This long-held concept of maintaining a constant cross-sectional velocity through a precipitator chamber stems primarily from the generally accepted Deutsch equation which holds that the highest percent efficiency in a system of parallel precipitators is attained when each precipitator handles a proportion of the total 'gas commensurate with the proportion of the size of the individual precipitator to the total. This concept and the equation, however, are based upon a uniform distribution of dust particles in the gas stream, such as when it enters the precipitator chamber.

SUMMARY OF THE INVENTION The present invention involves a significant departure from the accepted theory and practice of providing uniform flow rates across the cross section of a drytype horizontal precipitator. In particular, the accepted practice fails to take into account the fact that as dust particles are dislodged from their respective collecting electrodes, they fall some distance before being reentrained, thereby resulting in a greater concentration of particles flowing and being collected near the bottom of the chamber at greater distances downstream from the inlet. This effect is cumulative in character, with the dust concentration increasing farther along the flow stream because reprecipitated particles are constantlybeing re-entrained until they finally fall into the hoppers or are released from the precipitator with the cleaned air. The net result is that an increasingly greater quantity of particles must be collected on the lower portion of the collecting electrodes at greater distances from the inlet in the downstream direction of flow.

Therefore, to attain maximum collection efficiency the overall velocity of the gas stream at the entrance to the precipitator should be uniform (assuming a uniform distribution of particles), as is the accepted practice, but the velocity of gas flowing near the bottom of the precipitator chamber should be decreased in relation to the velocity of gas flowing near the top as the flow progresses through the chamber in order to compensate for the cumulative effect of re-entrainment and the tendency for the dust to settle as it flows through the precipitator. To put it another way, the ratio of the veloc ity of the gas flowing near the top of the chamber to the velocity of gas flowing near the bottom should increase, the further downstream the gas flows.

There is provided, in accordance with the invention, a novel and improved system for controlling gas flow in dry-type horizontal-flow electric precipitators. The system is based on the provision of one or more gas diverter units located between the inlet and outlet of the precipitator chamber. Each diverter unit includes a member extending transversely across the chamber to provide a resistance to gas flow at the bottom of the chamber so that gas flowing near the bottom of the chamber is diverted upwardly. Hence the velocity of gas flowing near the bottom of the chamber is decreased, relative to the velocity of gas flowing near the top, as the gas flows past the diverter unit.

The diverter unit may take various forms. For example, a simple and effective form is a single baffle that extends upwardly from the bottom of the housing and tranversely to the direction of gas flow and leaves an opening between the top of the baffle and the top of the housing through which the gas diverted by the baffle flows. Another form is a plurality of graded elongated baffles spaced one over another with each baffle extending transversely across the chamber and each pair of adjacent baffles defining an opening between them, the openings between each pair of adjacent baffles being larger the greater distance they are from the bottom of the chamber.

Other exemplary forms of diverter units are orifice plates having graded openings and inclined baffles which are set at different angles to vary the effective openings between adjacent ones. The latter form of diverter offers an opportunity for readily adjusting the openings to suit given conditions.

For short precipitators, a single diverter unit can significantly enhance operational efficiency. For longer units, however, it is preferable to provide two, three or more units spaced longitudinally from each other and defining in the flow chamber a multiplicity of sections, each of which contains groupings of emitter and collector electrodes. To compensate for the cumulative effect of repeated re-entrainment and a re-precipitation of particles in the downstream direction, the amount of gas deflected upwardly is increased as the gas flows past each-succeeding deflector unit. By lowering the velocity of gas near the bottom of the chamber, the particles dislodged from the collecting electrodes are able to fall a greater distance before becoming re-entrained or falling into the hoppers located at the bottom of the chamber. This is done to decrease the incidence of reentrainment in the downstream direction of flow.

Because of the cumulative effect, more gas is diverted upwardly as the gas flows past each succeeding deflecting unit to increase the ratio of the velocity of gas flowing near the top of the chamber in relation to the velocity flowing near the bottom. This ratio increase can either be linear or exponential in character, but for a more effective increase in collection efficiency the latter is preferable.

DESCRIPTION OF THE DRAWINGS For a better understanding of the invention, reference may be had to the following description of the exemplary embodiments, taken in conjunction with the accompanying drawings in which:

FIG. 1 is a cross-sectional view of an electric precipitator equipped with baffle-type flow diverters, portions of the view being broken out to limit repetition;

FIG. 2 is a cross-sectional front view of the electric precipitator of FIG. 1, again with portions being broken out, taken generally along a plane designated by the lines 22 in FIG. 1, and in the direction of the arrows;

FIG. 3 is a side schematic view of a precipitator which has diverter units of the flat baffle type;

FIG. 4 is a side schematic view of a precipitator which has diverter units of the inclined baffle type;

FIG. 5 is a partial perspective view in schematic form of several of the baffles illustrated in FIG. 4;

FIG. 6 is a side schematic view of a precipitator having diverter units of the orifice plate type; and

FIG. 7 is a pictorial view of an orifice plate of the type shown in FIG. 6, portions being broken out to restrict repetition.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS Referring to FIGS. 1 and 2, the electric precipitator is generally designated by reference numeral 10. Gas at a substantially uniform cross-sectional velocity, illustrated by arrows 11 in FIG. 1, is introduced into a flow chamber 12, which is defined by the housing of the electric precipitator 10, through an inlet opening 14. The gas flows past a plurality of emitting electrodes 16 and collecting electrodes 18, which extend substantially vertically within the chamber 12 and across the path of gas flow.

The emitter electrodes are charged to a high DC voltage, and the resultant field between emitter and collector electrode pairs ionizes the dust particles in the flow ing gas stream and charges them with the polarity of the emitting electrodes 16. The charged particles are attracted to the collecting electrodes 18, and accumulate on them. To dislodge the collected particles, the collecting electrodes 18 are periodically vibrated or rapped causing the collected particles to fall downwardly toward the bottom of the chamber 12 into dust collectors or hoppers 20. Because of the rapid flow rate of the gas stream and the relatively small size of the particles, a significant fraction of them will re-enter the gas stream, i.e., be re-entrained, at a lower level in the stream and will again be collected farther downstream as the gas flows toward the outlet opening 22.

In the embodiment of the invention shown in FIG. 1, the emitting and collecting electrodes 16 and 18 are arranged in the chamber 12 in separate groupings, designated by numeral 24, along the path of gas flow. A diverter unit 26 is positioned at the downstream end of each grouping 24 for diverting upwardly gas flowing near the bottom of the chamber 12 so that the velocity of gas flowing adjacent the bottom of the chamber 12 is decreased in relation to the velocity of gas flowing near the top.

Although in the' precipitator 10 shown in FIG. 1 a number of diverter units 26 are positioned longitudinally within the chamber 12 to prevent the flowing gas from reassuming its uniform flow, in relatively short precipitators a single unit can be used. In other precipitators the number of the units 26 can be varied depending on the size of the precipitator 10 and the flow characteristics of the gas. The primary purpose of the diverter units 26 is to induce a non-uniform flow as described above and to either maintain the velocity gradient or increase it along the direction of flow, as will be discussed below.

The diverter unit 26 shown in FIGS. 1 and 2 is constitute'd by a plurality of elongated baffles 28 spaced one over another. Each baffle 28 extends transversely across the chamber 12, and each pair of adjacent baffles 28 defines between them an opening 30. The baffles 28 can be attached along the end of the collecting electrodes 18 as shown in FIGS. 1 and 2, or they can be attached to the precipitator housing in any other suitable manner. The openings 30 are graded in that they are larger in their vertical dimension, the greater distance they are from the bottom of the chamber 12. As illustrated, all of the baffles 28 are identical, but baffles of different sizes could be used to accomplish essentially the same results.

The graded openings cause gas flowing adjacent the bottom of the chamber 12 to be diverted upwardly as the gas flows past each diverter unit 26 and establish a velocity gradient vertically within the chamber 12. The sizes of the openings 30 can be adjusted so that the velocity of gas flowing past each diverter unit 26 is varied as a function of the distance from the bottom of chamber 12, either linearly or exponentially. The latter has been found to be the most satisfactory for increasing collection efficiency of the precipitator 10.

By slowing down the velocity of gas flowing near the bottom of the chamber 12 in relation to the velocity of gas flowing near the top, the collected particles that are dislodged from the collecting electrodes 18 are able to fall a greater distance in the chamber 12 before becoming re-entrained or falling into the hopper 20, thereby reducing the incidence of re-entrainment and increasing collection efficiency.

However, re-entrainment of falling particles still occurs, resulting in the concentration of particles near the bottom of the chamber 12 being greater than the concentration near the top. To counteract this cumulative effect, the openings in each succeeding diverter unit 26 along the direction of gas flow are adjusted to divert a greater amount of gas upwardly so that the ratio of the velocity flowing near the top of the chamber 12 to the velocity of gas flowing near the bottom is increased as the gas flows past each succeeding diverter unit 26. This ratio increase can be accomplished in various ways, such as by decreasing the size of the openings 30 nearer the bottom of the chamber 12 in each succeeding diverter unit 26 in relation to the corresponding openings 30 in the immediately preceding diverter unit 26, or by similarly increasing the size of the openings 30 near the top of the chamber 12 in each succeeding diverter unit 26, or by simultaneously increasing and decreasing the openings near the top and bottom, respectively, of the succeeding diverter units 26. The main purpose for so varying the openings is to divert more of the flowing gas upwardly as it flows past each succeeding diverter unit 26.

A simple but effective embodiment of the invention is shown in FIG. 3 where each diverter 26 is a single baffle 32 that extends upwardly from the bottom of the housing 12 and transversely to the direction of gas flow, illustrated by arrows 11. An opening 34 is formed between the top of each baffle 32 and the top of the chamber 12 through which gas adjacent the bottom of the chamber 12 is directed for creating the velocity gradients discussed above as gas flows past each diverter unit 26. To create the ratio increase discussed above with regard to another embodiment of the invention, each succeeding baffle 32 is higher than the immediately preceding one so that a greater amount of the gas is diverted upwardly as it flows past each succeeding diverter unit 26.

FIGS. 4 and 5 illustrate another embodiment in the invention in which each diverter unit 26 includes baffles 36 that are inclined at graded angles, as designated by the reference numeral in FIG. 5. The baffles 36 that are nearer the bottom of the chamber 12 are more steeply inclined than those nearer the top, so that the openings 38 formed between each pair of adjacent baffles 36 are larger, the greater distance they are from the bottom of the chamber 12.

Similarly to the other embodiments of the invention discussed above, the velocity ratio can be increased as gas flows past each succeeding diverter unit 26 by increasing the angles of inclination 40 of the baffles 36 nearer the bottom of the chamber 12 in each succeeding diverter unit 26 in relation to the angles 40 of corresponding baffles 36 in the immediately preceding diverter unit, or by similarly decreasing the angles 40 near the top of the chamber 12 in each succeeding unit 26, or by doing both simultaneously. 5

Because the baffles 36 are inclined as described above, the gas flowing past each diverter 26 is diverted upwardly along the faces of the baffles 36, thereby allowing for a smoother flow within the chamber 12. A desirable characteristic of this type of diverter unit structure is that each baffle 36 can be pivotally attached to the sides of the precipitator housing in a way so that they can be adjusted to different gas flow conditions.

In the embodiment of the invention shown in FIGS. 6 and 7, each diverter unit 26 is an orifice plate 42 which can be used to divert the flowing gas in the manner described above. The orifice plate 42 is disposed within substantially the entire path of gas flow and perpendicular to it. The plate 42 includes a plurality of openings 44 with the areas of the openings 44 being greater the greater the distance they are from the bottom of the chamber 12.

FIG. 7 shows the openings 44 as being generally round and arranged in horizontal rows, with the same number of openings 44 being included in each row and arranged along substantially the same vertical center lines. However, the openings 44 in each diverter unit 26 may be of different shapes and may be arranged in different configurations and accomplish the same results. Similarly to the other embodiments of the invention, the openings nearer the bottom and top of the chamber 12 in succeeding diverter units 26 can be decreased and/or increased, respectively, in size in relation to corresponding openings 44 in each preceding diverter unit 26, either separately or simultaneously, as discussed above with regard to the other embodiments.

Thus, there is provided in accordance with the invention a novel and improved gas flow control system for horizontal, dry-type precipitators. The embodiments of the invention described above are intended to be merely exemplary and those skilled in the art will be able to make numerous variations and modifications, in addition to those mentioned above, without departing from the spirit and scope of the invention. All such variations and modifications are intended to be included within the scope of the invention, as defined in the appended claims.

I claim:

1. In a horizontal flow, dry-type electric precipitator of the type that includes a housing defining a flow chamber with an inlet at one end for receiving dustcontaminated gas into the chamber, an outlet at the other end for discharging cleaned gas, at least one dust collector in the bottom for receiving dust particles removed from the gas, and a plurality of emitting and collecting electrodes extending substantially vertically through the chamber across the path of gas flow, a gas flow control comprising:

a. at least one gas diverter which is disposed intermediate of said inlet and said outlet and which includes a multiplicity of vertically spaced-apart surfaces and openings therebetween, said surfaces extending generally transversely across the chamber with at least a portion of one of the surfaces being located adjacent the bottom of the chamber; and

b. the areas of said openings being greater, respectively, the more remote said openings are from the bottom of said chamber such as to provide a velocity gradient, whereby the velocity of gas flowing through the chamber increases as a function of the distance from the bottom of the chamber.

2. A precipitator according to claim 1, wherein the areas of the openings are graded such that the velocities of gas streams flowing past the diverter unit are linear functions of the distances they are from the bottom of the chamber.

3. A precipitator according to claim 1, wherein the areas of the openings are graded such that the velocities of gas streams flowing past the diverter unit are exponential functions of the distances they are from the bottom of the chamber. 4

4. A precipitator according to claim 1, wherein said surfaces comprise a plurality of elongated baffles and said baffles are spaced one over another to define said openings therebetween.

5. A precipitator according to claim 4, wherein the baffles are inclined at angles to the axis of the chamber and the baffles near the bottom of the chamber are more steeply inclined than those nearer the top such that the openings are larger the greater distance they are from the bottom of the chamber.

6. An electric precipitator according to claim 1, wherein:

a. there is a multiplicity of said diverters spaced lon gitudinally from each other and defining in the flow chamber a multiplicity of sections, each of which contains groupings of emitter and collector electrodes; and

b. each diverter includes a baffle that extends upwardly from the bottom of the housing and extends transversely to the direction of gas flow, and an opening is formed between the top of the baffle and the top of the housing through which the diverted gas flows, and each succeeding baffle is of a greater vertical dimension than the immediately preceding one, thereby causing each succeeding opening to be shorter in its vertical dimension than the immediately preceding one for increasing the ratio of velocity of gas flowing near the top of the chamber to the velocity of gas flowing near the bottom as gas flows past each succeeding diverter.

7. In a horizontal flow, dry-type electric precipitator of the type that includes a housing defining a flow chamber with an inlet at one end for receiving dustcontaminated gas into the chamber, an outlet at the other end for discharging cleaned gas, at least one dust collector in the bottom for receiving dust particles re-' moved from the gas, and a plurality of emitting and collecting electrodes extending substantially vertically through the chamber across the path of gas flow, a gas flow control comprising:

a. a gas diverter disposed intermediate of said inlet and said outlet, said diverter including an orifice plate which is disposed within substantially the entire path of flow and substantially perpendicular thereto; and

b. said plate including a plurality of spaced-apart openings, and the area of said plate included as openings being greater the greater the distance from the bottom of the chamber.

8. A precipitator according to claim 7, wherein the degree of gradation of the openings in each succeeding diverter in the downstream'direction of flow is greater so that the velocity gradient of gas flowing past each succeeding diverter is increasingly greater than the gradient for the immediately preceding one, whereby the ratio of the velocity of gas flowing near the top of the chamber is increased in relation to the velocity of gas flowing near the bottom as gasflows past each succeeding diverter.

9. In a horizontal flow, dry-type electric precipitator of the type that includes a housing defining a flow chamber with an inlet opening at one end for receiving dust-contaminated gas into the chamber, an outlet opening at the other end for discharging cleaned gas, at least one dust collector in the bottom for receiving dust particles removed from the gas, and a plurality of emitting and collecting electrodes extending substantially vertically through the chamber across the path of gas flow, a gas flow control comprising a multiplicity of gas diverters spaced longitudinally from each other and defining in the flow chamber a multiplicity of sections, each of which contains groupings of emitter and collector electrodes, each diverter including a plurality of elongated baffles spaced one over another, each baffle extending transversely across the chamber and each pair of adjacent bafi'les defining an opening between them, the opening between each pair of adjacent baffles being of greater vertical dimension the farther such opening is from the bottom of the chamber.

10. A gas flow control in accordance with claim 9, wherein the openings nearer the bottom of the chamber in each succeeding gas diverter are of lesser vertical dimension in relation to corresponding openings in the immediately preceding diverter such that the ratio of the velocity of gas flowing near the top of the chamber to the velocity of gas flowing near the bottom is increased as gas flows past each succeeding diverter.

11. A gas flow control in accordance with claim 9, wherein the openings nearer the top of 'the chamber in each succeeding gas diverter are of greater vertical dimension in relation to corresponding openings in the immediately preceding diverter such that the ratio of the velocity of gas flowing near the top of the chamber to the velocity of gas flowing near the bottom is increased as gas flows past such succeeding diverter.

12. A gas flow control in accordance with claim 9, wherein the openings located nearest both the top and bottom of the chamber in each succeeding diverter unit are of increased and decreased vertical dimensions, respectively, in relation to corresponding openings in the immediately preceding diverter for increasing the ratio of the velocity of gas flowing near the top of the chamber to the velocity of gas flowing near the bottom as gas flows past each succeeding diverter.

13. In a horizontal flow, dry-type electric precipitator of the type that includes a housing defining a flow chamber with an inlet opening at one end for receiving dust-contaminated gas into the chamber, and an outlet opening at the other end for discharging cleaned gas, at least one dust collector in the bottom for receiving dust particles removed from the gas, and a plurality of emitting and collecting electrodes extending substantially vertically through the chamber across the path of gas flow, a gas flow control comprising a multiplicity of diverters spaced longitudinally from each other and defining in the flow chamber a multiplicity of sections, each of which contains groupings of emitter and collector electrodes, each diverter including a plurality of inclined bafiles spaced one over another, each baffle extending transversely across the chamber, each pair of adjacent baffles defining an opening between them, and the baffles near the bottom of the chamber being more steeply inclined than those near the top such that openings are larger the greater distance they are from the bottom of the chamber.

14. A gas flow control in accordance with claim 13, wherein the bafiles near the bottom of the chamber in each succeeding gas diverter are more steeply inclined than the ones in the immediately preceding diverter such that the openings nearer the bottom of the chamber in each succeeding diverter are smaller in relation to the corresponding openings in the immediately preceding diverter for increasing the ratio of the velocity of gas flowing near the top of the chamber to the velocity of gas flowing near the bottom as gas flows past each succeeding diverter.

15. A gas flow control in accordance with claim 13, wherein the baffles near the top of the chamber in each succeeding gas diverter are less steeply inclined than the ones in the immediately preceding diverter such that the openings nearer the top of the chamber in each succeeding diverter are larger in relation to the corresponding openings in the immediately preceding diverter for increasing the ratio of the velocity of gas flowing near the top of the chamber to the velocity of gas flowing near the bottom as gas flows past each succeeding diverter.

16. A gas flow control in accordance with claim 15, wherein baffles near the bottom of the chamber in each succeeding gas diverter are more steeply inclined than the ones in the immediately preceding diverter such that the openings nearer the bottom of the chamber in each succeeding diverter are smaller in relation to the ducts in the immediately preceding deflecting unit.

17. In a horizontal flow, dry-type electric precipitator of the type that includes a housing defining a flow chamber with an inlet opening at one end for receiving dust-contaminated gas into the chamber, an outlet opening at the other end for discharging cleaned gas, at least one dust collector in the bottom for receiving particles removed from the gas, and a plurality of emitting and collecting electrodes extending substantially vertically through the chamber across the path of gas flow, a gas flow control comprising a multiplicity of gas diverters spaced longitudinally from each other and defining in the flow chamber a multiplicity of sections, each of which contains groupings of emitter and collector electrodes, each diverter including an orifice plate disposed within substantially the entire path of flow and substantially perpendicular thereto, the plate including a plurality of openings, the area of the plate included as openings being greater the greater the distance from the bottom of the chamber.

18. A gas flow control in accordance with claim 17, wherein the plate includes a plurality of rows of openings, with the openings in each row being substantially the same size and along the same substantially horizontal center line, and each row including the same number of openings arranged along the same substantially vertical center lines.

19. A gas flow control in accordance with claim 17, wherein the openings nearer the bottom of the chamber in each succeeding gas diverter are smaller than the ones in the immediately preceding diverter for increasing the ratio of the velocity of gas flowing near the top of the chamber to the velocity of gas flowing near the bottom as gas flows past each succeeding diverter.

20. A gas flow control in accordance with claim 17, wherein the openings near the top of the chamber in each succeeding gas diverter are larger than the ones in the immediately preceding diverter for increasing the ratio of the velocity of gases flowing near the top of the chamber to the velocity of gases flowing near the bottom as gas flows past each succeeding diverter.

21. A gas flow control in accordance with claim 17, wherein the openings near the top and bottom of the chamber in each succeeding gas diverter are larger and smaller, respectively, than the openings in the immediately preceding diverter for increasing the ratio of the velocity of gases flowing near the top of the chamber to the velocity of gases flowing near the bottom as gas flows past each succeeding diverter. 

1. In a horizontal flow, dry-type electric precipitator of the type that includes a housing defining a flow chamber with an inlet at one end for receiving dust-contaminated gas into the chamber, an outlet at the other end for discharging cleaned gas, at least one dust collector in the bottom for receiving dust particles removed from the gas, and a plurality of emitting and collecting electrodes extending substantially vertically through the chamber across the path of gas flow, a gas flow control comprising: a. at least one gas diverter which is disposed intermediate of said inlet and said outlet and which includes a multiplicity of vertically spaced-apart surfaces and openings therebetween, said surfaces extending generally transversely across the chamber with at least a portion of one of the surfaces being located adjacent the bottom of the chamber; and b. the areas of said openings being greater, respectively, the more remote said openings are from the bottom of said chamber such as to provide a velocity gradient, whereby the velocity of gas flowing through the chamber increases as a function of the distance from the bottom of the chamber.
 2. A precipitator according to claim 1, wherein the areas of the openings are graded such that the velocities of gas streams flowing past the diverter unit are linear functions of the distances they are from the bottom of the chamber.
 3. A precipitator according to claim 1, wherein the areas of the openings are graded such that the velocities of gas streams flowing past the diverter unit are exponential functions of the distances they are from the bottom of the chamber.
 4. A precipitator according to claim 1, wherein said surfaces comprise a plurality of elongated baffles and said baffles are spaced one over another to define said openings therebetween.
 5. A precipitator according to claim 4, wherein the baffles are inclined at angles to the axis of the chamber and the baffles near the bottom of the chamber are more steeply inclined than those nearer the top such that the openings are larger the greater distance they are from the bottom of the chamber.
 6. An electric precipitator according to claim 1, wherein: a. there is a multiplicity of said diverters spaced longitudinally from each other and defining in the flow chamber a multiplicity of sections, each of which contains groupings of emitter and collector electrodes; and b. each diverter includes a baffle that extends upwardly from the bottom of the housing and extends transversely to the direction of gas flow, and an opening is formed between the top of the baffle and the top of the housing through which the diverted gas flows, and each succeeding baffle is of a greater vertical dimension than the immediately preceding one, thereby causing each succeeding opening to be shorter in its vertical dimension than the immediately preceding one for increasing the ratio of velocity of gas flowing near the top of the chamber to the velocity of gas flowing near the bottom as gas flows past each succeeding diverter.
 7. In a horizontal flow, dry-type electric precipitator of the type that includes a housing defining a flow chamber with an inlet at one end for receiving dust-contaminated gas into the chamber, an outlet at the other end for discharging cleaned gas, at least one dust collector in the bottom for receiving dust particles removed from the gas, and a plurality of emitting and collecting electrodes extending substantially vertically through the chamber across the path of gas flow, a gas flow control comprising: a. a gas diverter disposed intermediate of said inlet and said outlet, said diverter including an orifice plate which is disposed within substantially the entire path of flow and substantially perpendicular thereto; and b. said plate including a plurality of spaced-apart openings, and the area of said plate included as openings being greater the greater the distance from the bottom of the chamber.
 8. A precipitator according to claim 7, wherein the degree of gradation of the openings in each succeeding diverter in the downstream direction Of flow is greater so that the velocity gradient of gas flowing past each succeeding diverter is increasingly greater than the gradient for the immediately preceding one, whereby the ratio of the velocity of gas flowing near the top of the chamber is increased in relation to the velocity of gas flowing near the bottom as gas flows past each succeeding diverter.
 9. In a horizontal flow, dry-type electric precipitator of the type that includes a housing defining a flow chamber with an inlet opening at one end for receiving dust-contaminated gas into the chamber, an outlet opening at the other end for discharging cleaned gas, at least one dust collector in the bottom for receiving dust particles removed from the gas, and a plurality of emitting and collecting electrodes extending substantially vertically through the chamber across the path of gas flow, a gas flow control comprising a multiplicity of gas diverters spaced longitudinally from each other and defining in the flow chamber a multiplicity of sections, each of which contains groupings of emitter and collector electrodes, each diverter including a plurality of elongated baffles spaced one over another, each baffle extending transversely across the chamber and each pair of adjacent baffles defining an opening between them, the opening between each pair of adjacent baffles being of greater vertical dimension the farther such opening is from the bottom of the chamber.
 10. A gas flow control in accordance with claim 9, wherein the openings nearer the bottom of the chamber in each succeeding gas diverter are of lesser vertical dimension in relation to corresponding openings in the immediately preceding diverter such that the ratio of the velocity of gas flowing near the top of the chamber to the velocity of gas flowing near the bottom is increased as gas flows past each succeeding diverter.
 11. A gas flow control in accordance with claim 9, wherein the openings nearer the top of the chamber in each succeeding gas diverter are of greater vertical dimension in relation to corresponding openings in the immediately preceding diverter such that the ratio of the velocity of gas flowing near the top of the chamber to the velocity of gas flowing near the bottom is increased as gas flows past such succeeding diverter.
 12. A gas flow control in accordance with claim 9, wherein the openings located nearest both the top and bottom of the chamber in each succeeding diverter unit are of increased and decreased vertical dimensions, respectively, in relation to corresponding openings in the immediately preceding diverter for increasing the ratio of the velocity of gas flowing near the top of the chamber to the velocity of gas flowing near the bottom as gas flows past each succeeding diverter.
 13. In a horizontal flow, dry-type electric precipitator of the type that includes a housing defining a flow chamber with an inlet opening at one end for receiving dust-contaminated gas into the chamber, and an outlet opening at the other end for discharging cleaned gas, at least one dust collector in the bottom for receiving dust particles removed from the gas, and a plurality of emitting and collecting electrodes extending substantially vertically through the chamber across the path of gas flow, a gas flow control comprising a multiplicity of diverters spaced longitudinally from each other and defining in the flow chamber a multiplicity of sections, each of which contains groupings of emitter and collector electrodes, each diverter including a plurality of inclined baffles spaced one over another, each baffle extending transversely across the chamber, each pair of adjacent baffles defining an opening between them, and the baffles near the bottom of the chamber being more steeply inclined than those near the top such that openings are larger the greater distance they are from the bottom of the chamber.
 14. A gas flow control in accordance with claim 13, wherein the baffles near the bottom of the chamber in each succeeding gas diverteR are more steeply inclined than the ones in the immediately preceding diverter such that the openings nearer the bottom of the chamber in each succeeding diverter are smaller in relation to the corresponding openings in the immediately preceding diverter for increasing the ratio of the velocity of gas flowing near the top of the chamber to the velocity of gas flowing near the bottom as gas flows past each succeeding diverter.
 15. A gas flow control in accordance with claim 13, wherein the baffles near the top of the chamber in each succeeding gas diverter are less steeply inclined than the ones in the immediately preceding diverter such that the openings nearer the top of the chamber in each succeeding diverter are larger in relation to the corresponding openings in the immediately preceding diverter for increasing the ratio of the velocity of gas flowing near the top of the chamber to the velocity of gas flowing near the bottom as gas flows past each succeeding diverter.
 16. A gas flow control in accordance with claim 15, wherein baffles near the bottom of the chamber in each succeeding gas diverter are more steeply inclined than the ones in the immediately preceding diverter such that the openings nearer the bottom of the chamber in each succeeding diverter are smaller in relation to the ducts in the immediately preceding deflecting unit.
 17. In a horizontal flow, dry-type electric precipitator of the type that includes a housing defining a flow chamber with an inlet opening at one end for receiving dust-contaminated gas into the chamber, an outlet opening at the other end for discharging cleaned gas, at least one dust collector in the bottom for receiving particles removed from the gas, and a plurality of emitting and collecting electrodes extending substantially vertically through the chamber across the path of gas flow, a gas flow control comprising a multiplicity of gas diverters spaced longitudinally from each other and defining in the flow chamber a multiplicity of sections, each of which contains groupings of emitter and collector electrodes, each diverter including an orifice plate disposed within substantially the entire path of flow and substantially perpendicular thereto, the plate including a plurality of openings, the area of the plate included as openings being greater the greater the distance from the bottom of the chamber.
 18. A gas flow control in accordance with claim 17, wherein the plate includes a plurality of rows of openings, with the openings in each row being substantially the same size and along the same substantially horizontal center line, and each row including the same number of openings arranged along the same substantially vertical center lines.
 19. A gas flow control in accordance with claim 17, wherein the openings nearer the bottom of the chamber in each succeeding gas diverter are smaller than the ones in the immediately preceding diverter for increasing the ratio of the velocity of gas flowing near the top of the chamber to the velocity of gas flowing near the bottom as gas flows past each succeeding diverter.
 20. A gas flow control in accordance with claim 17, wherein the openings near the top of the chamber in each succeeding gas diverter are larger than the ones in the immediately preceding diverter for increasing the ratio of the velocity of gases flowing near the top of the chamber to the velocity of gases flowing near the bottom as gas flows past each succeeding diverter.
 21. A gas flow control in accordance with claim 17, wherein the openings near the top and bottom of the chamber in each succeeding gas diverter are larger and smaller, respectively, than the openings in the immediately preceding diverter for increasing the ratio of the velocity of gases flowing near the top of the chamber to the velocity of gases flowing near the bottom as gas flows past each succeeding diverter. 